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E Duval

Publications and source records attributed to E Duval.

At least 19 recordsLinked to original sources
PubMed2005

Intrinsic vibrational coherence in face-centered cubic supra-crystals of silver nanocrystals: Raman scattering measurements.

The ordering of silver nanocrystals is tuned from amorphous aggregates to highly well-ordered, face-centered cubic supra-crystals, using various substrates and controlling their temperature to obtain this. Low-frequency Raman scattering, for the first time, demonstrates vibrational coherence in fcc supra-crystals of nanocrystals. This is shown by a narrowing of the peak corresponding to the quadrupolar modes of the nanocrystals. However, this is obtained when the supra-crystals are smaller than the excitation wavelength. When the supra-crystals are larger, the narrowing cannot be observed. Furthermore, for any size of the supra-crystals, a shift to low frequency of the Raman peak due to the Lorentz field effect is seen.

Journal Article↗
PubMed2005

Vibrational coherence of self-organized silver nanocrystals in f.c.c. supra-crystals.

Fabrication of devices from inorganic nanocrystals normally requires that they are self-organized into ordered structures. It has now been demonstrated that nanocrystals are able to self-organize in a 'supra'-crystal with a face-centred cubic (f.c.c.) structure. The physical properties of nanocrystals self-organized into compact arrays are quite different from those of both isolated nanocrystals and the bulk phase. The collective optical and magnetic properties of these nanocrystal assemblies are governed mainly by dipolar interactions. Here, we show that nanocrystals vibrate coherently when they are self-organized in f.c.c. supra-crystals. Hence, a phase relation exists between the vibrations of all of the nanocrystals in a supra-crystal. This vibrational coherence can be observed by a substantial change of the quadrupolar low-frequency Raman scattering peak. Although a change in electronic transport properties has previously been observed on self-organization of silver nanocrystals, vibrational coherence represents the first intrinsic property of f.c.c. supra-crystals.

Journal Article↗
PubMed2002

High-frequency dynamics of the glass former dibutylphthalate under pressure.

The high-frequency dynamics of a fragile molecular glass former (dibutylphthalate) was studied through inelastic x-ray scattering (IXS), as a function of pressure and temperature. The mesoscopic structural arrest associated with the glass transition process was tracked by following upon cooling the inelastic excitations at fixed Q points in the dispersion curves, at ambient pressure and 2 kbar. The application of pressure to this system induces an offset between the macroscopic glass transition temperature T(g) and the mesoscopic glass transition temperature, as determined from IXS. The concomitant fragility decrease of dibutylphthalate under pressure unveils that the stronger the glass former is, the more its mesoscopic dynamics differ from the macroscopic regime. This trend is interpreted as the signature of a nanoscopic inhomogeneous elastic network. Further aspects of this system are obtained when studying the temperature dependence of its nonergodicity factor f(Q)(T). The chemical specificity of the molecule is suggested to be responsible for the nonobservation of a critical temperature T(c) in dibutylphthalate up to approximately 300 K.

Journal Article↗
PubMed2000

A possible role of the Na(+)/K(+)-ATPase for O(2) production from H(2)O(2).

We are attempting to supply a new insight on interaction between Na(+)/K(+)-ATPase and H(2)O(2). We demonstrate that in vitro the Na(+)/K(+)-ATPase, a non heme-protein, is able to disproportionate H(2)O(2) catalatically into dioxygen and water, as well as C(40) catalase. By polarography, we quantify O(2) production and by Raman spectroscopy H(2)O(2) consumption. A comparative analysis of kinetics parameters relative to O(2) production shows that for Na(+)/K(+)-ATPase the affinity of the catalytic site able to transform H(2)O(2) into O(2) is twice weaker than that for C(40) catalase. It also shows that the molar activity for O(2) production is 300-fold weaker for ATPase than for catalase. Inhibitors, pH and GSH studies highlight the differences between the heme- and nonheme-proteins. Indeed, for C(40), NaN(3) is strongly inhibiting, but much less for ATPase. The pH range for the catalatic activity of ATPase is wide (6.5 to 8.5), while it is not for C(40) catalase (optimum at pH 8). The Na(+)/K(+)-ATPase catalatic activity is reduced in presence of glutathione, while it is not the case with C(40) catalase.

Animals↗
PubMed1999

Snow algae of the Sierra Nevada, Spain, and High Atlas mountains of Morocco.

Snow algae (Chlorophyta) are reported from the Sierra Nevada mountains in southern Spain and the High Atlas mountains of Morocco. Populations of the snow algae Chlamydomonas sp., coloring the snow orange-red, were collected from Pico de Veleta, Spain, while snow samples from Mt. Neltner in the High Atlas mountains, contained resting spores of an orange-green colored Chloromonas sp. Other microbes observed in snow samples include bacteria, fungi, heterotrophic euglenids, diatoms, nematodes, and heterotrophic mastigotes (flagellated protists). This is the first report of snow algae from the Sierra Nevada mountains of Spain and from the Afro-alpine environment.

Altitude↗
PubMed1995

Can biological homochirality result from a phase transition?

The problem of chiral purity in living organisms is still one of the prominent difficulties in the study of the origins of life. In particular the parity non-conservation known to occur in weak interactions could not be related to this lack of symmetry: these physical forces, though universal, are very weak and up to now no amplification process had been proposed. In 1991, A. Salam remarked that, due to the attractive character of the parity violating force in electro-weak interactions, a phase transition at low temperature should exist, leading eventually to enantiomeric purity. We undertook then a series of experimental tests, looking for a sizeable change in the optical activity of cystine molecules. We found no evidence for the phase transition down to 0.01 K. The interpretation of these negative results will be discussed, and future experiments proposed.

Amino Acids↗
PubMed1994

Jumping translocation in a newborn boy with dup(4q) and severe hydrops fetalis.

We report on the unusual cytogenetic findings in a newborn boy with severe hydrops fetalis. He has a mosaic for 2 unbalanced chromosome rearrangements: a der(18)-t(4;18)(q31;q23) and a der(18)t(4;18)(q31;p11). As a result, this patient had a duplication of 4q31-qter in all cells, and was possibly monosomic for the distal ends of 18p and 18q, respectively in the 2 cell lines. Since in both rearrangements the same chromosome 4 segment was translocated to 2 different chromosome regions, we consider the present finding as a peculiar type of jumping translocation.

Abnormalities, Multiple↗